1. Field
The present invention relates to a shift controller, particularly relates to a shift controller of a sequential type transmission that turns a shift drum with an electric motor.
2. Description of the Related Art
A sequential type multispeed transmission which is based upon a multispeed transmission provided with plural transmission gear pairs, which drives a predetermined transmission gear and a predetermined sleeve by a shift fork fitted to a shift drum. The shift fork switches the engagement of a dog clutch provided between transmission gears and executes a shift. In addition, a configuration that enables an automatic shift or a semi automatic shift by driving the shift drum and a clutch of such a multispeed transmission with an electric motor is known.
The shift drum and the transmission gear are ordinarily lubricated by lubricating oil. The temperature of the lubricating oil varies depending upon outside air temperature, the heat of an engine, and other factors. When the viscosity of the lubricating oil varies according to the variation of the temperature, the revolution speed of the shift drum may vary even if the same driving signal is applied to the electric motor for the shift drum. A change of the revolution speed of the shift drum may have an effect on noise and shift effect when the dog clutch is engaged.
JP Patent No. 2903932 (JP '932) discloses a shift controller that drives a step motor for changing the transmission gear ratio of a friction roller type continuously variable transmission at normal speed when the temperature of lubricating oil is equal to or below a predetermined value, and drives the step motor at lower speed than the normal speed when the temperature of the lubricating oil exceeds the predetermined value.
However, when technique disclosed in JP '932 is applied to the above-mentioned sequential type multispeed transmission, the technique has a problem that time from the start of a shift till the completion of the shift varies according to the variation of the temperature of lubricating oil. Therefore, for example, when the temperature of lubricating oil is high, it takes much time to shift in response to an instruction of a shift and a response may be deteriorated. Further, in a transmission that switches the engagement of a dog clutch configured by a dog tooth and a dog slit and shifts speed, as the engagement of the dog clutch that establishes the current speed is required to be released at an initial stage of a shift, it may be difficult to release the engagement of the dog clutch when the revolution speed of a shift drum is reduced in the whole section from the start of a shift till the completion thereof.